The present invention relates to a thermosensitive recording system capable of preventing excessive temperature elevation of its heat-emitting recording head in operation.
In a conventional thermosensitive recording system, for instance, in a conventional signal-reception apparatus of a facsimile apparatus, thermosensitive recording sheets capable of forming images upon application of heat thereto, are employed for recording received information, and images are formed thereon by a heat-emitting recording head.
In the signal-reception apparatus, one group of image signals, for instance, black image signals, are recorded on the thermosensitive recording sheets by applying heat thereto through the heat-emitting recording head. Therefore, the greater the quantity of image signals recorded by the heat-emitting recording head, the greater the quantity of heat generated per unit time by the heat emitting recording head. Therefore, when many black image signals are contained in the information recorded, it may occur, in the extreme case, that the temperature of the recording head is so elevated that the whole surface of the recording sheet is colored by the heat generated by the recording head. Or, the resistors for generating heat in the recording head could be damaged, resulting in complete failure in recording.
In order to avoid such dangers, in the conventional thermosensitive recording system, it is necessary to stop the system from time to time depending upon the quantity of the image signals to be reproduced by the heat-emitting head. Yet, in the conventional thermosensitive recording system, if the operator is careless in such operation, damaging the recording head is all too likely.
In order to eliminate the above-mentioned shortcomings of the conventional thermosensitive recording system, there has been proposed a method of preventing excessive elevation of the overall temperature of the heat-emitting recording head by reducing the pulse width of the signals which cause elevation of the temperature of the recording head, for instance, the signals for the above-mentioned black images, or by decreasing the power necessary for such signals. This method, however, has a shortcoming in that images with high contrast cannot be obtained when the temperature of the recording head is comparatively low and the quantity of heat generated by the recording head is small.